A shocking one quarter of all shark and ray species are threatened with extinction, according to the results of a new study.

The great white shark is classified as Vulnerable on the IUCN Red List

Threat analysis

The paper, published this week in the open-access journal eLife, analysed the threat and conservation status of an impressive 1,041 species of chondrichthyans, a fascinating group of fish species including sharks, rays, skates and chimaeras whose skeletons are made of cartilage rather than bone. The results were rather alarming, revealing that this group is among the most threatened in the animal kingdom.

The paper is the result of collaboration between more than 300 experts from 64 countries, and reports that, while no species has yet been driven to global extinction, at least 28 populations of skates, sawfishes and angel sharks are now locally or regionally extinct. In addition, several shark species have not been seen for several decades.

Reef manta ray parts are highly valued in traditional medicine, posing a threat to this majestic species

Threat hotspots

The study highlights two areas which are currently experiencing a higher than expected level of threat: the Red Sea and the Indo-Pacific Biodiversity Triangle. The latter is considered to be among the most biologically and culturally diverse regions on the planet, yet unfortunately it is also one of the least regulated.

The authors of the paper explain that, “The Indo-Pacific Biodiversity Triangle, particularly the Gulf of Thailand, and the islands of Sumatra, Java, Borneo, and Sulawesi, is a hotspot of greatest residual threat, especially for coastal sharks and rays with 76 threatened species.”

It is feared that, should no national or international action be taken, these species could rapidly become extinct.

Finning was revealed to be a major threat to many shark species

Major threats

The results of the study revealed that the main threat to chondrichthyans is overexploitation through targeted fisheries and incidental catches. Of particular concern for the future of sharks, wedgefishes and sawfishes is the process of ‘finning’, which is driven by the huge market demand for shark fin soup, a highly sought-after delicacy in China.

The authors of the new research paper state that, “Fins, in particular, have become one of the most valuable seafood commodities. It is estimated that the fins of between 26 and 73 million individuals, worth US$400-550 million, are traded each year.”

Habitat loss is a further threat to chondrichthyans, with 22 species being threatened by the destruction of estuaries and river systems for the purposes of residential and commercial development, and 12 species being placed at risk due to the conversion of mangroves into shrimp farms. In addition, pollution and climate change have been identified as major threats to sharks, rays and their relatives.

The scalloped hammerhead shark is classified as Endangered on the IUCN Red List

Additional factors

As well as providing a vital insight into the type and extent of threats to chondrichthyans, the paper also revealed other interesting factors which come into play. It was found that large body size and occurrence in shallow habitat are the biggest factors determining a species’ likelihood of being threatened. The results showed that with every 10-centimetre increase in a species’ maximum body length came a 1.2-percent increase in the probability that the species would be threatened. Dwellers of deep water appear to fare better than their shallow-water relatives, with a 10.3-percent decrease in the probability of being threatened for every 50-metre increase in the minimum depth limit of the species.

The observance of Thanksgiving Day is primarily associated with the United States, and is a tradition which is thought to date back to colonial times following the safe arrival of the first European settlers to the untamed shores of North America. Nowadays, families and friends congregate to give thanks for what they have, so to celebrate Thanksgiving in our own wild way, we’ve gathered together a few of nature’s special inhabitants that we think owe each other thanks: symbiotic species!

Exclusive residence

Common clownfish are able to live among the tentacles of stinging sea anemones

Simply speaking, symbiotic species are those that interact in some way, to the benefit of one or both of the critters in question. A classic example, and one that many Disney fans will be familiar with, is the relationship that exists between clownfish and sea anemones.

Sea anemones usually sting fish that come into contact with their tentacles, but clownfish have developed a clever, yet rather gross, method of disguise. By covering its skin in mucus, the clownfish can trick the anemone into thinking it is touching itself, and so does not get stung. In return for a safe place to live and food in the form of debris and parasites found amongst the anemone’s tentacles, the clownfish is thought to scare away fish that may prey upon the anemone, and even lure fish in for its tentacled home to eat – a classic win-win situation! The clownfish is also believed to provide the anemone with good water circulation through fanning its fins as it swims around.

Did you know?

There are different kinds of symbiotic relationships. Some benefit both species involved, and are known as ‘mutualistic’ symbioses, whereas ‘parasitic’ relationships are those in which one species profits at the expense of the other. In some cases, one species benefits but the other is affected neither positively nor negatively, and these are known as ‘commensalistic’ symbioses.

Nutritious nectar and pollen parcels

Bees, such as this small garden bumblebee, play an important role in plant pollination

Bees feed on pollen and nectar sourced from a variety of flowering plants, with honey bees using the nectar to make their sticky, sugary treat. Although flowers appear to lose out by ‘donating’ nectar, they actually benefit from these flying visits. As a bee rummages around the flower head for food, some pollen gets stuck to its hairy body and legs, and this accidental cargo is then transferred to the next flower the insect visits, pollinating it and enabling the plant to reproduce.

Did you know?

The traditional origin of the modern Thanksgiving Day is commonly thought to be the festivities that occurred at the Plymouth Plantation in Massachusetts in 1621, when the European settlers celebrated their safe voyage, peace and good harvest. However, there is some evidence to suggest that Spaniards in Florida were the first to truly celebrate Thanksgiving back in 1565.

Getting a little peckish…

Oxpeckers help remove parasites from large mammals such as this roan antelope

In the wilds of the African savanna, large mammals such as this roan antelope can quickly become covered in ticks and all sorts of other creepy crawlies, which doesn’t sound entirely pleasant! Luckily, help is at hand in the form of winged wonders known as oxpeckers. Oxpeckers are known to hitch a ride on the backs of a range of iconic species including hippos, buffalos, giraffe and various antelopes, gorging themselves on ticks, botfly larvae and other parasites – the mammals get cleaned, and the birds get fed, and so this has often been classified as a mutualistic relationship. However, more recent studies have shown that oxpeckers often pick at scabs and cuts to keep them open to get more food, subjecting the wounds to possible infection and potentially harming the host mammal, making this symbiotic relationship more of a parasitic one.

Helpful houseguests

Reef-building corals rely on tiny blue-green algae to survive

Reef-building corals provide homes for single-celled blue-green algae known as zooxanthellae, and in return these microscopic plants provide energy-containing compounds for the coral through the process of photosynthesis. The coral uses these vital compounds to build its calcium carbonate skeleton. In a way, these tiny blue-green algae are like live-in coral chefs…and they even clean up after themselves by removing any waste products! Brilliant!

Nature’s six-legged gardeners

Leaf-cutter ants tend to their fungus garden by creating ‘mulch’ from leaf fragments

Leaf-cutter ants are known as nature’s gardeners, as they spend their time foraging for leaves and cutting them into suitably sized fragments before transporting them back to their huge underground nests where the leaves are used to cultivate a fungus garden. While the ant colony is entirely dependent upon this fungus supply for food and so greatly benefits from this situation, the fungus benefits by being cultivated by the ants but also loses out by being eaten, and so this relationship could be classified as a more commensalistic one.

Did you know?

Most of us think of the US in relation to Thanksgiving, but did you know that several other countries observe similar days, too? These include Canada, Puerto Rico and Liberia. Additionally, the city of Leiden in South Holland celebrates the traditional US Thanksgiving Day, making the Netherlands the only non English-speaking country to formally celebrate this particular occasion.

Food on the go…

Dugong

Loggerhead turtle

Leopard shark

Giant manta ray

Scientists are somewhat divided over whether the relationship that exists between specialised fish known as remoras and a variety of larger ocean species is a mutualistic or commensalistic one. Also known as suckerfish, remoras have a specially adapted first dorsal fin which has been modified into a sucker-like organ. Remoras use this to attach themselves to other marine animals such as sharks, rays, sea turtles and dugongs, feeding on material dropped by the host species while also getting a free ride and protection from potential predators. This seems rather one-sided, but some scientists believe that the remoras may also feed upon certain parasites on the host’s body or gills, therefore providing a great cleaning service to their marine meal providers.

If these beholden bovids, indebted invertebrates and contented chondrichthyans haven’t quenched your thirst for wild Thanksgiving-related information, why not check out last year’s blog, which features a whole host of awesome animals that the first European settlers might have seen upon arriving in North America.

The largest skate in the Northwest Atlantic Ocean, the barndoor skate can grow up to about 1.5 metres in length. Like other skates, this species has a flattened body which is fused to the expanded pectoral fins to form a broad disc. Its snout is pointed and its tail bears three rows of spines as well as two small dorsal fins. The barndoor skate grows slowly, taking at least 6 to 7 years to reach maturity, and can potentially live for up to 18 years. Its diet consists mainly of bottom-dwelling prey such as fish, squid, crustaceans, bivalves and worms. The eggs of the barndoor skate are laid in smooth, rectangular capsules and hatch after about 11 to 16 months.

Although not specifically targeted by fisheries, the barndoor skate has often been taken as accidental bycatch, and has been part of a group of several skates fished in U.S. waters which are not recorded by species. The flesh of this and other skates has been used as lobster bait, fish meal, pet food and seafood. The slow growth, late maturity and low reproductive rate of this species make it vulnerable to overfishing, and its population has undergone a dramatic decline. Possession of the barndoor skate in U.S. waters is now banned, and ‘no-take’ zones in areas such as Georges Bank have decreased mortality of this species and increased the number of juveniles being produced. A reduction in fishing effort is thought to have allowed the barndoor skate population to start recovering, but if fishing was to increase again the skate would be likely to decline once more.

Beyond the signature kangaroo or koala, did you know that Australia is also home to a wide range of lesser-known and somewhat bizarre-looking species such as the spotted handfish or the southern hairy-nosed wombat? With astounding habitats including Barrow Island, the Great Barrier Reef, and the outback, we thought we would take the opportunity to highlight just some of the unique species found in this spectacular land!

Weedy wader

The leafy seadragon is endemic to Australia, meaning it is found nowhere else on Earth. Living in shallow coastal waters, these slow-moving creatures call underwater seagrass meadows home, blending in perfectly due to their leaf-like appendages.

King croc

The largest of all crocodilians, the saltwater crocodile roams both the land and sea. By using its powerful tail and webbed hind feet, this species is an effective aquatic predator. The saltwater crocodile feasts on large land animals such as wallabies, dingoes, and even humans!

The face of climate change

Found only in northern Australia, the lemuroid ringtail possum may become Australia’s first victim of global climate change. Being unable to withstand temperatures over 86°F (30°C), this species is extremely vulnerable to heatwaves, which are expected to increase in frequency as the climate changes. In fact, a heatwave in 2005 was thought to have wiped out the entire population until a few individuals were finally discovered in 2009.

Misunderstood marsupial

Known for its frightening nocturnal screeches, the Tasmanian devil is the largest of the carnivorous marsupials. Contrary to its savage reputation, the Tasmanian devil is actually quite shy and is only aggressive when feeling threatened or when in competition with other devils.

Snack and swim

Strictly feeding on plants, the dugong is often referred to as the ‘sea cow’, but it is actually more closely related to elephants than cows! Found off the coast of northern Australia, the dugong uses its flexible upper lip to rip whole plants apart, leaving ‘feeding trails’ on the sea floor. What a messy eater!

Water-free wallaby

Found throughout Australia, the black-footed wallaby lives its life in groups of 10 to 100 individuals. Found primarily in rock piles and granite outcrops, this wallaby feasts mostly on grasses and fruit, and, interestingly, obtains nearly all of its water through its food.

Burrow builder

An expert digger, the southern hairy-nosed wombat is able to construct burrows that support a constant inside temperature of 78°F in the summer and 57.2 °F in the winter. These burrows are often formed as networks of up to thirty meters long that can host five to ten wombats.

Smooth sailing

The softly furred sugar glider uses the membrane along its body to glide distances of up to 150 feet between trees. This agile possum also has a rather distinctive alarm call, which is said to resemble a yapping dog!

Cultural croaker

Found only in the northern Australian Alps and the Australian Capital Territory, the northern corroboree frog has a local cultural story attached to its name. ‘Corroboree’ is an aboriginal word used to describe a gathering, where traditionally attendees are adorned with brightly colored yellow markings similar to those of this frog.

Aquatic ambler

A fish with ‘hands’ that can walk the ocean floor? It’s true! The spotted handfish, one of the world’s most endangered fish, is able to use its characteristic ‘hand-like’ fins to walk the sea floor, occasionally sucking on prey like shrimp and small fish. Threatened by development, a restricted distribution and a low reproductive rate, the spotted handfish population may be restored in the future through successful re-introduction programs.

If you’re looking to continue your ‘walkabout’ around Australia on ARKive, check out the new Barrow Island topic page or search the 1,200+ Australian species on ARKive today. Feel free to share your favorite Aussie species in the comments below!

A significant improvement in the health of seagrass in a central Californian estuary is due to the return of sea otters, according to recent research.

Researchers have found that the presence of sea otters may be improving the health of seagrass beds

Seagrass decline

Seagrass has been suffering drastic declines worldwide, and coastal California is no exception. Urbanisation has led to a massive increase in nutrient pollution along the state’s coast, with run-off from fields treated with nitrogen-rich fertilisers being blamed for the reduction in seagrass beds in the region. However, new research has revealed that the return of sea otter populations to the area may be enabling seagrass levels to recover.

Sea otters were hunted to near extinction in the late 19th and early 20th centuries, mainly for their dense pelt which was extremely sought-after for the fur trade. This latest research, published in the journal Proceedings of the National Academy of Sciences (PNAS), suggests that the drastic reduction in sea otter numbers may have exacerbated the decline of seagrass in the region.

Sea otters are now returning to the area, and, despite the continued pollution of the ocean, the water-dwelling plants are now doing much better. It is thought that the return of sea otters has triggered a complex ecological chain reaction which favours the survival of seagrass.

Sea otters feed on crabs and other shellfish

Seagrass saviour

Scientists assessed seagrass levels in part of Monterey Bay, California, over the past 50 years, mapping increases and declines. A whole host of factors which could potentially affect seagrass levels were studied, but the only one which matched the recorded changes was sea otter numbers. The health of the marine ecosystem relies upon a delicate balance of predator and prey species, and scientists have theorised that it is a readjustment in this balance that is now enabling seagrass to thrive.

Increased nutrients in the ocean due to fertiliser run-off have favoured the growth of a particular type of algae which grows on seagrass, shading the leaves and causing them to die off. Ordinarily, this algae is kept in check by small invertebrates which feed upon it, but with the reduction in sea otters came an increase in one of its main food sources – crabs. Crabs feed on marine invertebrates, so higher numbers of crabs meant fewer invertebrates to keep algae levels down, therefore contributing to the drastic reduction in seagrass.

Testing the hypothesis

To test their theory, the researchers set up experiments in similar estuaries with and without sea otters, and carried out other tests in the field as well as in the lab. One experiment involved putting cages on the seagrass, with some being accessible to sea otters and some not. The results of the tests confirmed the hypothesis.

Sea otters

Fighting climate change

Brent Hughes, lead author of the study, described seagrass as being ‘the canary in the coalmine’, as it can be used to predict the levels of nutrient pollution in the water. He marvelled at the positive effect the return of the sea otters is having, saying, “This estuary is part of one of the most polluted systems in the entire world, but you can still get this healthy thriving habitat, and it’s all because of the sea otters. So it’s almost like these sea otters are fighting the effects of poor water quality.”

Seagrass plays an extremely important role in the marine ecosystem, acting as a nursery habitat for a wide variety of fish species, and taking in carbon dioxide from the water and the atmosphere, therefore potentially helping in the fight against climate change. In addition to this, seagrass contributes to the stability and protection of the shoreline.

“It’s what we call a foundation species, like kelp forest, salt marsh or coral reef,” said Hughes. “The major problem from a global perspective is that seagrass is declining worldwide. And one of the major drivers of this decline has been nutrient inputs from anthropogenic sources, via agriculture or urban runoff.”

Benefits

A ban on sea otters that was in place to prevent them from impinging on fisheries in the southern California area was lifted last year, and so the findings from this latest research are particularly relevant.

“That’s important because there’s a lot of these kind of degraded estuaries in southern California because of all the urban runoff from places like Los Angeles and San Diego,” said Hughes. “Coastal managers will now have a better sense of what’s going to happen when sea otters move into their systems. There’s a huge potential benefit to sea otters returning to these estuaries, and into these seagrass beds that might be threatened.”